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Full text of "Alaskan glacier studies of the National Geographic Society in the Yakutat Bay, Prince William Sound and lower Copper River regions"

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CHILDS  GLACIER                                         413
its position, however, it is out of harmony with any other uneroded rock spurs along the Copper River, though perfectly normal as a morainic accumulation of Childs Glacier. Repeated traverses of its slopes have revealed no rock ledges, and no rock in place is found in the existing exposures. The first of these is at the extreme eastern end, where the grading for the Copper River and Northwestern Railway cut into the end of the moraine for f of a mile. Here all of the material was till, with large bowlders imbedded in fine clay. The other exposure is at the western end of the moraine, where Childs Glacier has cut into the edge of the moraine terrace, revealing no rock, but till and stratified gravel. These relationships prove that this is a morainic accumulation and not a rock hill, and it is also clear that this is a moraine built by Childs Glacier and not by the former trunk glacier of the Copper River canyon.
There is a gap of a mile and a half between this large northern ridge and the next two remnants of the terminal moraine of Childs Glacier. They are each small knobs, lying obscurely in the forest between the railway and Miles Glacier. The northernmost is a small hillock, rising to a height of 802 feet, or over 100 feet above the adjacent outwash plain. It lies just in the edge of a more-recent, low, terminal moraine of Miles Glacier (PI. CLXV) and is made up partly of rounded gravels. The other small residual of the terminal moraine of Childs Glacier is a long, low ridge which probably marks the easternmost portion of the former bulb.
The fourth hilly area which represents part of the terminal moraine of Childs Glacier is fairly large, but does not rise very high above the outwash plain. It extends from the railway to the Copper River, beginning with a single, steep-sided ridge which crosses the railway west of Mile Post 47. Close to the railway, it is a narrow, sinuous ridge, esker-like in places, but generally with knobs and kettles, and, at one locality, divided into parallel ridges which enclose the basin of a large pond. Near the railway it rises 25 to 40 feet above the adjacent plain of outwash gravels, which is perfectly smooth except where trenched by parallel, southwest-trending channels of the former streams from Miles Glacier. This moraine broadens and becomes more irregular as it extends southwestward and, near the Copper River, rises to an elevation of 100 to 200 feet.
The fifth and southernmost remnant of this terminal moraine lies south of Childs Glacier and west of Copper River, which has cut a steep cliff in it. The moraine is 210 feet high and extends close up to the present margin of Childs Glacier (PL CLXV).
The expanded bulb of Childs Glacier, which built this terminal moraine, was at least 4^ miles wide and projected 1| miles farther east in the Copper River valley than the present ice front. The time of its maximum independent expansion was later than the stage of a trunk glacier in Copper River valley, and must have also been a time of diminution of the present bulb of Miles Glacier, which overlaps it in part. The Childs Glacier evidently retained this advanced position for an exceedingly long time in order to produce these large morainic accumulations. The Copper River necessarily flowed then on the eastern side of its valley. The latest shifting of the Copper River towargl the western side of the valley, doubtless at a time of expansion of the Miles Glacier bulb, resulted in the cutting away of portions of this terminal moraine, as well as in the destruction of the ice bulb of Childs Glacier. Subsequently the outwash gravels were deposited between the moraine remnants by streams from Miles Glacier, and the Copper River was forced over to its present course, where it undercuts the front of Childs Glacier and prevents its terminus from expanding into a symmetrical bulb.